Cepheids in LMC clusters and the period-age relation

Abstract

We have made a new comparison of the positions of Cepheids and clusters in the LMC and constructed a new empirical period-age relation taking into account all available data on Cepheids in the LMC bar provided by the OGLE project. The most probable relation is logT=8.50−0.65 logP, in reasonably good agreement with theoretical expectations. Numerous Cepheids in rich clusters of the LMC provide the best data for comparing theories of stellar evolution and pulsation and the dynamical evolution of clusters with observations. These data suggest that stars undergoing their first crossing of the instability strip are first-overtone pulsators, though the converse is true of only a small fraction of first-overtone stars. Several rich clusters with suitable ages have no Cepheids—a fact that is not understood and requires verification. Differences in the concentration of Cepheids toward their cluster centers probably reflect the fact that the clusters are at different stages of their dynamical evolution, with the Cepheids in cluster coronas being ejected from the cluster cores during dynamical interactions between stars.